Planner / Calendar to "block" specific assets in the future

[gitsask]

At this moment, there is no possibility to block certain items for checkout.
For example, if there is an event during the year, some people want to make a reservation of specific items in advance.
It should be nice to have the possibility to block items so it can't be checked out anymore when it is conflicting with a reservation in the future. So if i block an item from 1st to 30th of July. And i trie to checkout that item on the 10th of June with return date of 10th of july, this should give an error or warning. Or if i checkout an item that has a reservation/blocking in the future, but i'm not specifying a "estimated time of checkin", i should also receive a warning.
At this moment, the 'requestable items' feature is not very usable. The only thing it does is sending an email that user X requested item Y.

[snipe]

This is a duplicate of #5081 (or at least directly related)